1. Technical Field of the Invention
The present invention relates to a method and apparatus for controlling power generated by a generator for vehicles, and in particular, to the method and apparatus for controlling the power generation based on a gradual excitation technique which requires the generator to be control on gradually changed excitation currents after its start.
2. Prior Art
In vehicles that run with a driving force, the conditions of an on-vehicle engine immediately after its start are unstable. On the other hand, immediately after the start, a power generation control unit on the vehicle allows an increase of excitation current of the engine-driven generator and allows commencement of power generation in order to raise voltage of the battery to a predetermined level. Upon commencement of power generation, torque of the generator is Increased, which tends to cause failure in starting the engine at low temperatures particularly in a cold morning, for example.
Generally known power generation control units for vehicles include one, for example, in which gradual excitation is performed by gradually increasing the excitation current (i.e., gradually exciting technique) at the time of starting to suppress drastic increase of drive torque of the generator, and to improve startability. In such a generation control unit, the gradual excitation is carried out as required, not only at the time of starting the engine, but also when an electric load(s) (i.e., current consumer) has increased. Japanese Unexamined Patent Application Publication No. 6-311798 discloses a generation control unit for vehicle, in which, compared to gradual excitation control performed for an increase in the amount of the load during the normal generation control (i.e., control except for the engine start), a rate of increasing the excitation current is decreased during gradual excitation when an internal combustion engine is started.
In cases where power consumption of current consumers is further increased during such a gradual excitation operation, under which the magnitude of power generation is suppressed, the voltage of the battery is considerably reduced, likely to disable the operations of the current consumers. If an engine control unit is disabled, the engine is stopped.
In contrast, Japanese Unexamined Patent Application Publication No. 9-107640, for example, discloses a power generation control unit for vehicle, in which the gradual excitation is cancelled when the voltage of the battery is reduced to not more than a predetermined voltage to drastically increase the excitation current, so that the battery is suppressed from reducing voltage.
Since power consumption of an engine starting system is very large, battery voltage is significantly reduced at an engine start. In the power generation control unit disclosed in Japanese Unexamined Patent Application Publication No. 9-107640 mentioned above, during a gradual excitation at an engine start, the gradual excitation is cancelled due to such a battery voltage reduction, so as to drastically increase the excitation current. Therefore, drive torque of the generator is also drastically increased, which may cause the engine in an unstable state to stop.